If you change your plan before the cut off date, your new plan will start on the 2nd of next month. Otherwise, it will start on the 2nd of the following month.
For Example:
In a case where plan change cut-off date is 24 Jan: plan change requests submitted on or before 24 Jan will be activated by 2 Feb. Plan change requests made by 25 Jan and after will be activated by 2 Mar.